How can data on an unrooted phone be backed up?If you are talking about the application data, it is a security design that other apps can not read this data unless the have super user permissions (root). Everything else can be backed up.

Disable low-battery warning, specifically on XOOMthe sound is in system, an app would have to be root to replace it, doing what you said is your best bet. Disabling the notification all together needs to be edited in the framework. You can not yet do this on the Xoom sorry.

Data Vault apps with Unlock PatternYes you could from 4 points, but you would also be able to figure out how the generated it from 4 points, the amount of possible codes would be something like 5! a really really low number.